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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 56 (1970), No. 5

  • 随想

    pp. 505-506

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  • Re-oxidation Behaviors of Sponge-Irons Reduced from Ferric Oxide and Iron-Ores

    pp. 507-520

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    Some characteristics of sponge-irons reduced from ferric oxide and iron-ores were studied. They were reduced by hydrogen in the temperature range 400 to 800°C and re-oxidized by N2-O2 mixed gases at 400°C. The results were as follows.
    1) In most cases, sponge-irons reduced in the range 600 to 700°C showed maximum re-oxidation degrees.
    2) The re-oxidation degree of those sponge-irons was increased with increasing the oxygen concentration of oxidizing atmosphere.
    3) When the sponge-irons reduced at 600°C were reheated at 700°C, re-oxidation showed lower values than that reduced at 700°C.
    4) The behaviors of the re-oxidation were studied for several kinds of iron-ores. The sponge-irons reduced from limonite ores which have large surface areas, showed high re-oxidation degrees up to 90%.
    Those from hematite ores were also re-oxidized up to 40-60%, those from magnetite ores, however, have small surface areas and lower re-oxidation degrees up to 10-20%. Although pyrite cinders have generally small surface areas, those sponge-irons showed high re-oxidation degrees.
    5) Re-oxidation degrees of sponge-irons could be considered to be controlled by such factors as specific surface area, lattice strain, pore distribution and temperature rise by the heat of re-oxidation.
    The factor of temperature is particularly important for low temperature re-oxidation.
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    Readers Who Read This Article Also Read

    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • Solubility of Hydrogen in Liquid Iron Alloys

    pp. 521-535

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    The solubility of hydrogen in liquid pure iron and liquid binary iron alloys has been measured by Sieverts' method and by the sampled method.
    By Sieverts' method the solubility of hydrogen in liquid Fe-C-Si alloys has also been measured.
    The results obtained by Sieverts' method are summarized as follows:
    (1) Solubility of hydrogen in liquid pure iron:
    (2) Interaction parameter in liquid binary iron alloys:
    (3) The experimental results on activity coefficients of hydrogen in liquid Fe-C-Si alloys are in rather good agreement with the values calculated by using Wagner's equation than those obtained by the graphical method.
    The solubility of hydrogen obtained by the sampled method shows the satisfactory agreement with the value obtained by Sieverts' method in the case of Fe-Cr, Fe-Mn and Fe-Mo alloys, but distinct difference is shown in Fe-S alloys.
  • Activity of Silicon in Liquid Iron and the Effect of Carbon on the Activity of Silicon

    pp. 536-545

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    The thermodynamic properties of silicon in liquid iron and iron-carbon solution have been studied by distribution experiments at 1450°C and 1540°C. The data in iron-silicon system are in good agreement with those of the previous studies above 0.2 atom fraction of silicon in liquid iron, while they showed somewhat lower values under 0.2 atom fraction of silicon. Data on heat of mixing by KÖRBER and OELSEN are applied to extend the present results to 1600°C. The interaction parameters difined as ∂ ln γS1/∂NS1 were the values of 19.2 at 1450°C, 17.5 at 1540°C and 17.0 at 1600°C in the concentration range from 0.2 to 0.35 atom fraction.
    Liquid iron-silicon-carbon alloys are equilibrated with iron-silicon alloy through the liquid bridge of silicon-silver alloy. The results obtained are consistent with the data by SCHROEDER and CHIPMAN.
    Interaction parameter εCS1 was 21.0 at 1450°C when the value of εS1S1=19.2 was applied.
  • Effect of Scrap Melting on Temperature and Concentration of Carbon of Molten Steel in LD Converter

    pp. 546-557

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    A mathematical model for determining the variations of a temperature of molten steel, tm and a concentration of carbon in steel bath, Cm caused by the melting of scamp fed into LD converter is developed in this work.
    Experimental data obtained by others in the blowing process of LD converter were plotted on the figure of Cm vs. tm. It was noted from this figure that there were considerable differences between the data for the case where scrap had not been fed into converter and those with feed of scrap, and that the data obtained where all of scrap had not yet been molten indicated the variation of Cm with tm along a liquidus line of the iron-carbon phase diagram in accordance with the progress of the blowing time.
    Behaviors of Cm and tm accompanied by the fluctuations of these process variables caused by the changes of operating conditions were analysed in terms of the model mentioned above. And, on the basis of these behaviors, a method of a end-point dynamic control with the aid of a topological phase diagram was proposed in this paper.
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    Readers Who Read This Article Also Read

    1. Mineral Composition of Dolomite-fluxed Pellets and Its Effect on the Contraction during Reduction up to 1100°C Tetsu-to-Hagané Vol.67(1981), No.6
  • Theoretical Analysis on the Degassing Process by Rising Bubbles

    pp. 558-568

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    A mathematical model for degassing process by rising bubbles is developed on the basis of material and heat balances in gas phase and material balance in liquid phase. From this model, the volume of inert gas which is necessary to degass hydrogen, oxygen and carbon in molten steel down to the required concentrations can be estimated.
    The effects of the initial diameter of inert gas bubble, the depth of blowing point of inert gas, the pressure of gas at the surface of molten steel, the residence time of rising bubble and the concentration ratio of carbon to oxygen on the degassing rate and on the concentrations of CO and H2 in rising bubble were determined by numerical calculations of the model with the aid of digital computer.
  • Effect of Nb or/and V Addition and the Amounts of Extracted Carbides on the Strengthening of Hot Rolled Steels

    pp. 569-590

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    An investigation was made on the strengthening of as-rolled steels by Nb or/and V addition in termsof the amounts of precipitates of NbC and V4C3. The steels are of two levels of carbon content, 0·05% and 0·18%, and contain 0-0.10% Nb or/and 0-0.20% V. The steels were vacuum melted andhot-rolled to 7mm in thickness through 8 passes and partly 2 passes.
    The observations by electron microscope were also carried out on the thin foil specimens and theNbC particles extracted from the steels. The features of the precipitates which had an effect onstrengthening of steels were discussed and the new method was adopted to fractionate the NbC precipitatedin ferrite matrix from the total extracted NbC. The main results were as follows:
    (1) The strengthening per unit addition of Nb, Δσ/%Nb, was nearly the same in the 0·05%Cand0·18%C-steels, but that of V, Δσ/%V increased with C content. Regardless of C content, Δσ/%Nb was greater than Δσ/%V.When compared with the 0·18%C-steels, the features of carbide precipitation in the 0·05%C-steelswere as follows: In the Nb-steels, much amounts of NbC were extracted as the precipitates in ferritematrix and NbC lined up in rows became observable. In the V-steels, both the amounts of V4C3 andthe chance to find out the lined-up V4C3 decreased.
    (2) The strengthening by simultaneous addition of Nb and V was over the sum of the individualstrengthening in the 0·05%C-steels and below the sum in the 0·18%C-steels. The addition of Nb tothe 0·05%C-V-steels resulted in the increase of the extracted amounts of V4C3 and raised the probabilityto find out the fine carbides in row.
    All these results can be explained consistently each other in terms of the thermodynamical data onthe carbides in steels, the observed transformation temperature of the steels and the precipitation mechanism of the carbides effective to strengthening of ferrite matrix.
    x

    Readers Who Read This Article Also Read

    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • The Effects of Chromium and Silicon on the Corrosion of Steels by V2O5 and V2O5-Na2SO4 Mixtures

    pp. 591-606

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    In order to make clear the effects of alloying elements, especially chromium and silicon, on the corrosion of steels by V2O5 and V2O5-Na2SO4 mixtures, the corrosion resistance of Cr steels, Cr-Ni steel, Cr-Si steel and Cr-Ni-Si steel was examined by weight loss, metallography, X-ray diffraction and electron beam X-ray microanalysis. The main results obtained are as follows:
    1. The corrosion resistance of the steels against molten V2O5 at 850°Cwas increased by the addition of more than 18% Cr, but less improved by the addition of 12% Cr. This was explained to be due to the differences in properties and constitutions of the scales. The corrosion resistance of Cr steels was increased by the addition of 3% Si. This effect was considered to be due to the formation of SiO2 layers in the scales. The enrichment of Ni was observed at the base metal-scale interface of corroded 18% Cr-8% Ni steel, which showed a fairly good corrosion resistance. The existence of CrχFe1-χVO4solid solution in Fe2O3-Cr2O3-V2O5 ternary system was suggested by X-ray diffraction. This solid solution was found in the corrosion products of Cr-Si steels and 18% Cr-8% Ni steel.
    2. The corrosion resistance of steels against molten V2O5-Na2SO4 mixture (10: 1 by weight ratio) at 850°C was less improved by the addition of 18-21% Cr, but increased by the addition of about 60% Cr. The resistance of Cr steels was improved by the addition of about 3% Si. The effect was considered to be due to the formation of SiO2 layers in the scales.
    8% Cr-3% Si steel, which showed a fairly good resistance against the molten mixtures containing 0-30mol% Na2SO4, showed less resistance against the mixtures more than 40 mol% Na2SO4. This difference was considered to be due to the lack of protective SiO2 layers.
  • New Intermitted Type Billet Cooling Bed

    pp. 607-613

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    The paper presented the studies of billet cooling bed and the development of new intermitted cooltype billet cooling bed at the Yawata Works of Yawata Iron & Steel Co. By the use of new coolingdevice, the cooling capacity of cooling bed was improved, especially the deformation of billet during cooling was almost eliminated.
  • Development of Siteel (High-strength Fe-Si alloy containing 3·5-7% Si)

    pp. 614-621

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    “Siteel”, denominated by the author in 1959, is defined as follows: Siteel is a high strength Fe-Sialloy containing less than 0·025% C, more than 2·3% Si, some amount of Mn, Ni, Cr, Mo, etc., andthe balance essentially Fe, in which the total amount of the Ni and Mn is varied so as to approach twotimes of the Si content to lower the Ac3 transformation point below 750°(1400°F), thereby preventingthe alloy from grain-growth which usually lowers the toughness.
    This new alloy can be easily cast, rolled and cold-drawn and has many valuable characteristics whichare superior to those of alloy steels such as NiCrMo structural steel SNCM 1 (AISI 4337) and 18-8stainless steel SUS 32, (AISI 316). Consequently siteel can be beneficially used for various applicationsrequiring high strength and toughness, and at the same time excellent corrosion and erosion resistances.
    Siteel was produced on trial in some steel making plants, Kubota Iron Works and Japan Steel Works, with remarkable success.
    In this paper, the general characteristics and some typical applications of four kinds of siteel aredescribed, and new standards of 18-8 stainless steels containing 3-4% Si are proposed for realization of the industrial production of these high silicon alloys.
  • Structure of Grain Boundary

    pp. 622-635

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  • The Metallic Recuperators for Iron and Steel Works in Japan

    pp. 636-645

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  • 抄録

    pp. 646-655

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